Compute FFT from the input QPOE file.
input file: rp90_sti.qp
output files: rp90_ftp.tab, rp90_pwr.tab
In searching for short periods using a long data interval many bins are necessary [(no. of bins) = ] and generation of a _ltc.tab file may prove impractical. In such cases, the QPOE file may be input. Only the largest Fourier coefficients, but not the complete list of (e.g., ) coefficients should be used, so we set power_thresh to exclude all but the largest from the table [root]_pwr.tab. The normalization has been adjusted so the value of the power coefficient, normpower, does not depend strongly on number of bins or number of counts. A significant signal will have a value of for a 103 bin transform and a value of for 105 bins. Time required for a 105 bin transform is 2-3 minutes.
xt> fft.fftcoeff=no # don't generate a long list of coefficients xt> fft.power_thresh=7 # set the significance threshold xt> fft input source file (table or time-sorted qpoe file): rp90_sti.qp root name for output files [rrot_fft(ftp,pwr).tab]: rp90lng background qpoe file: <cr> input table column heading: src number of bins 2048 # The task uses the closest power of 2 to the input valueFFT done with 2048 bins!
creating histogram output file rp90_ftp.tab creating fft power output file rp90_pwr.tab